Tendinopathy is accompanied by a cascade of inflammatory events promoting tendon degeneration. Among various cytokines, interleukin-1β plays a central role in driving catabolic processes, ultimately resulting in the activation of matrix metalloproteinases and a diminished collagen synthesis, both of which promote tendon extracellular matrix degradation. Pulsed electromagnetic field (PEMF) therapy is often used for pain management, osteoarthritis, and delayed wound healing. In vitro PEMF treatment of tendon-derived cells was shown to modulate pro-inflammatory cytokines, potentially limiting their catabolic effects. However, our understanding of the underlying cellular and molecular mechanisms remains limited. We therefore investigated the transcriptome-wide responses of Il-1β-primed rat Achilles tendon cell-derived 3D tendon-like constructs to high-energy PEMF treatment. RNASeq analysis and gene ontology assignment revealed various biological processes to be affected by PEMF, including extracellular matrix remodeling and negative regulation of apoptosis. Further, we show that members of the cytoprotective Il-6/gp130 family and the Il-1β decoy receptor Il1r2 are positively regulated upon PEMF exposure. In conclusion, our results provide fundamental mechanistic insight into the cellular and molecular mode of action of PEMF on tendon cells and can help to optimize treatment protocols for the non-invasive therapy of tendinopathies.

Biodegradable and bioresponsive polymer-based nanoparticles (NPs) can be used for oligonucleotide delivery, making them a promising candidate for mRNA-based therapeutics. In this study, we evaluated and optimized the efficiency of a cationic, hyperbranched poly(amidoamine)s-based nanoparticle system to deliver tdTomato mRNA to primary human bone marrow stromal cells (hBMSC), human synovial derived stem cells (hSDSC), bovine chondrocytes (bCH), and rat tendon derived stem/progenitor cells (rTDSPC). Transfection efficiencies varied among the cell types tested (bCH 28.4% ± 22.87, rTDSPC 18.13% ± 12.07, hBMSC 18.23% ± 14.80, hSDSC 26.63% ± 8.81) and while an increase of NPs with a constant amount of mRNA generally improved the transfection efficiency, an increase of the mRNA loading ratio (2:50, 4:50, or 6:50 w/w mRNA:NPs) had no impact. However, metabolic activity of bCHs and rTDSPCs was significantly reduced when using higher amounts of NPs, indicating a dose-dependent cytotoxic response. Finally, we demonstrate the feasibility of transfecting extracellular matrix-rich 3D cell culture constructs using the nanoparticle system, making it a promising transfection strategy for musculoskeletal tissues that exhibit a complex, dense extracellular matrix.